1. Field of the Invention
The present invention relates to collets.
2. Description of the Prior Art
Tool bits having a screw thread at their rear end, are known. The threaded end of the tool bit engages a nut located in a collet, and by rotating the bit relative to the nut, the forward projection of the cutting end of the bit from the collet can be accurately set to the required value.
There is proposed in German Utility Model Specification No. 1,996,804 dated Aug. 3, 1968 a collet for a threaded-end tool bit, comprising a body split into a number of segments effective to grip the shank of the tool bit when the collet is clamped within a chuck. A cylindrical nut engaged with the threaded end of the tool bit is seated in the collet to the rear of the bit-engaging surfaces of the collet and is frictionally clamped by the segments. The rear end portion of the body is screw-threaded to receive a threaded member which carries a forwardly-directed spigot arranged to engage the rear end of the tool bit, and to locate positively the tool bit in its selected axial position in the collet. A pin extends from the threaded member into a recess in the nut to secure same against rotation.
In this collet, when the collet is clamped within the chuck, the bit-engaging nut is frictionally clamped within the collet. The radial gripping forces acting on the nut cause the bit-engaging surfaces of the collet to diverge slightly from the shank of the bit with the result that, in practice the collet only grips the bit at its forward end. Although this angle of divergence is small it is sufficient to permit vibration of the bit during use, and further, under certain circunstances the bit may slip.